You tend to handle number of arguments with this sort of logic:
IF "%1"=="" GOTO HAVE_0
IF "%2"=="" GOTO HAVE_1
IF "%3"=="" GOTO HAVE_2
etc.
If you have more than 9 arguments then you are screwed with this approach though. There are various hacks for creating counters which you can find here, but be warned these are not for the faint hearted.